The invention is related to means and a method for registering permeability of ducts or seam structures.
In operation tanks and other hollow structures need to be free of by-pass leakage. Often sufficient tank venting is needed, e.g. during or after being filled with a fluid which is highly volatile and thus gases out. For venting a connector or connector assembly consists of a single or several individual connectors, such as hose nipples to which separate flexible venting tubes are to be connected to collect the venting flow at a suitable location. Where plastics fuel tanks or the like are concerned each nipple is secured separate to the tanks wall outside by a joint such as a weld. The nipple passage is then connected to the tanks interior via an opening in the tank wall.
In producing the nipple or joint the flow cross-sections may be constricted or closed. Then no longer a sufficient volume flow rate of e.g. min. 40 or 50 l/min. for a given pressure gradient of max. 7 or 6 mbar can pass. For engine fuel tanks of internal combustion engines, especially on motor vehicles, a common flow capacity of all venting nozzles of e.g. approx. 60 l/min. at an overpressure of approx. 5 mbar in the fuel tank is specified. This capacity is thus to be tested before the tank is installed in the vehicle or before it is sealed tight. Instead of thus testing the tank when still dry, it may be tested after installation. Thus proper function or flow capacity of a tank venting system is tested during intentional operation of the filled tank. Soilage may constrict the flow cross-sections.
This test may be done by dynamic or dammed pressure testing. Thereby a gaseous test flow, such as air, is fed into the tank via the connector and any restriction in the connectors flow capacity is detected by way of an overpressure materializing in the test duct. Thereby a high pressure gradient needs to be generated. Thus, e.g., the overpressure in the test duct amounts to approx. 1 bar with the flow cross-section closed. Accordingly the flow capacity of perviousness can not be measured at a substantially lower pressure gradient of e.g. less than 200 or 50 mbar. Apart from this, generating the cited overpressure is technically expensive. The pressure flow results in very high volume flow rates and thus in very noisy test operation. Also sealing between the test duct and the tank connector is difficult under the high test pressure. With increasing flow cross-section of the tank connector the tests accuracy is diminished. This inaccuracy is already excessive at a flow cross-section of 30 mm2 corresponding to a passage diameter of 6 mm. However, the tank connectors to be tested may have significantly larger flow cross-sections of e.g. 80 mm2 corresponding to a passage diameter of 10 mm, of 115 mm2 corresponding to a diameter of 12 mm or of 155 mm2 corresponding to a diameter of 14 mm.
An object is to provide an apparatus and a method which obviate the disadvantages of known configurations. Another object is to enable precise testing even for large flow cross-sections. A further object is to permit testing of flow capacity under actual test conditions. Still another object is to keep consumption of the test medium low. A still further object is to carry out testing with little noise. An object is also to permit each individual connector to be sealingly connected to the test duct by simple means.
According to the invention a partial vacuum is applied for testing. In case of fully automated testing on a production line the tank is, in sequence, embedded in a holder positionally secured by tension, cut out to have openings in its wall, fitted with a connector body in the vicinity of each opening by welding or the like, before the flow capacity of this connection is then tested. The tank or connector may have more than 10, 20 or 30 such individual connectors. All of them are tested simultaneously and/or in sequence. For example, the tank may be equipped with several connectors in a welding station and then transported on the conveyor to the next welding station where further connectors are fitted. Testing the perviousness of the fitted connectors may already be done in the first or subsequent station whilst at the same time further connectors are fitted.
For reliable testing with partial vacuum or suction flow a very slight pressure gradient between the test duct and the tank chamber is sufficient. Thus deformation of the tank due to pressure gradient is avoided even when the dimensionally rigid tank has very thin walls. To further advantage compressed air consumption and noisiness are low. Producing a seal at the transition between the test duct and the tank connector is also reliable when the test duct during testing connects to the tank connector only by axial or radial pressure contact while being linearly removable. The perviousness can be directly measured as volume flow rate for a constant pressure gradient. In all of the flow cross-sections cited the measuring accuracy is very high.
A rated flow capacity, i.e. a minimum perviousness for intentional operation is set for each or all individual connectors of the tank. The low pressure of e.g. 5 mbar is selected so that it exists in the test duct when this rated flow capacity is given. Then a function or calibration curve is plotted which reproduces the relation between the low pressure and the volume flow rate. Changes in the low pressure are measured for a constant suction capacity and for variations in the effective flow cross-sections. Changes in the volume flow rate are measured at a constant low pressure while also varying the effective flow cross-sections. From the resulting calibration curve a measurement of the low pressure at constant suction capacity permits detecting whether the rated or minimum perviousness is given.
However, the test may also happen by directly measuring the volume flow rate in the test duct, if hereby the low pressure as put on is maintained constant.